This could be a problem if the user wants to offline a TailPage but dueto THP allocation failure, the HeadPage is offlined.

It may be better to only soft offline THPs if page ==compound_head(page). If page != compound_head(page), we still split THPslike before.

Because in migrate_pages(), we cannot guarantee any TailPages in thatTHP are migrated (1. THP allocation failure causes THP splitting, thenonly HeadPage is going to be migrated; 2. even if we change existingmigrate_pages() implementation to add all TailPages to migration listinstead of LRU list, we still cannot guarantee the TailPage we want tomigrate is migrated.).